Selenite

These samples of selenite are displayed in the Smithsonian Museum of Natural History. Selenite is a name given to clear crystals of gypsum, as contrasted with the milky, translucent gypsum that usually forms as evaporative deposits. The name comes from the Greek selene, meaning "moon", a reference to the whitish reflections off the crystal faces. Selenite exhibits beautiful crystals, but they are too soft to be considered as gemstones.